Electrodeposition of metal over large nonconducting surfaces

ABSTRACT

A method of electrodepositing metal on a large nonconducting surface involving the use of nonconductive surface having an exposed network of interconnecting electrical conductors. Methods of electroforming and electroplating involving the use of such a surface. A method of making an electroforming mold and an electrodeposition form with such a surface. An electroforming mold and an electrodeposition form with such a surface. An electroplated article having a base containing such a surface. A method of making a foraminous metal article utilizing such a surface.

United States Patent [72] inventor Siegfried G. Bart Montclair, NJ.

[21] Appl. No. 709,354

[22] Filed Feb. 29, 1968 [45] Patented Nov. 23, 1971 l 73] Assignee BartManufacturing Corporation Newark, NJ.

I54] ELECTRODEPOSITION OF METAL OVER LARGE NONCONDUCTING SURFACES 15Claims, 9 Drawing Figs.

[52] U.S.Cl 29/19L4, 204/9, 204/1 1, 204/12, 204/20, 204/25, 204/281 [51Int. Cl 823p 3/20, C23b 7/02. C23b 5/60 [50] Field of Search 204/2025,281,11,6,3,4,l2;29/191.4

[56] References Cited UNITED STATES PATENTS 1,589,564 6/1926 Robinson204/12 3,230,163 1/1966 Dreyfus 204/281 2,632,722 3/1953 Libberton 204/62,637,404 5/1953 Bart 204/20 2,776,253 1/1957 Scho1l.. 204/20 2,826,1433/1958 Muse 204/6 FOREIGN PATENTS 281,819 8/1965 Australia 363,4329/1931 Great Britain 204/20 481,785 3/1938 Great Britain 204/11 PrimaryExaminer-John H. Mack Assistant Examiner-T. Tufariello Allorney-Lane,Aitken, Dunner & Ziems ABSTRACT: A method of electrodepositing metal ona large nonconducting surface involving the use of nonconductive surfacehaving an exposed network of interconnecting electrical conductors.Methods of electroforming and electroplating involving the use of such asurface. A method of making an electroforming mold and anelectrodeposition form with such a surface. An electroforming mold andan electrodeposition form with such a surface. An electroplated articlehaving a base containing such a surface. A method of making a foraminousmetal article utilizing such a surface.

ELECTRODEIOSIT ION OF METAL OVER LARGE NONCONDUCTING SURFACES BACKGROUNDOF THE INVENTION a cathode in a electrolytic cell is used as a mold.When metal is electrodeposited on the conducting for the electrolysis,and it is made conducting by applying an electrically conducting coatingto the surface. This process, prior to the present invention, was along, tedious and questionable operation. Because the current had toflow through the thin conducting coating, which was not withoutsignificant resistance, electrodeposition began at the edge of thecoating where connection was made to the coating high current to betransmitted through a relatively thin conductive coating,

BRIEF SUMMARY OF THE INVENTION The system of the present inventionovercomes these problems of the prior art by providing an electricallyinterconnected network of electrical conductors Within and adjacent thesurface of the nonconducting portion of the cathodic mold. Prior to theapplication of a conductive coating, the surface of the cathodic mold islightly abraded to expose portions of the conductors in thenonconductive surface. An electrically conducting coating is thenapplied to the surface. This coating will contact the exposed conductorportions at a large number of points uniformly distributed over theentire surface on which electrodeposition is to take place. When theresulting cathodic mold is placed in the electrolytic bath forelectrodeposition on the conducting surface of the mold, electricalconnection to the mold is made through the conductors. As a result ofthe conductivity provided by such conductors, the electrodeposition willtake place at a uniform rate over the entire surface and high currentconcentration points on the conducting surface will be eliminated.Because of the uniform the time for depositing a given overall thicknessis greatly reduced.

Accordingly, an object of the present invention is to provide animproved method of electrodeposition over large nonconducting surfaces.

Another object of the present invention is to provide an improved methodof electroforming large articles.

A further object of the present invention is to facilitateelectrodeposition at a uniform rate over a large nonconducting surface.

A still further object of the present invention is to eliminate theproblem of high current concentrations in the electrodeposition of metalover large nonconducting surfaces.

A still further object of the present invention is to decrease the timeto electrodeposit a layer of metal to a given thickness over a largenonconducting surface.

A still further object of the present invention is to provide animproved mold for electrofonning.

A still further object of the present invention is to provide improvedelectrodeposited products.

A still further object of the present invention is to provide animproved method of electrofonning a foraminous article such as a screenand to provide an improved cathode for electroforming said article.

become readily apparent as the following detailed description of theinvention unfolds, the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of aplaster form used in one embodiment of the present invention;

FIG. 2 is an enlarged detailed sectional view illustrating a portion ofa cathodic mold of the present invention being manufactured on theplaster form of FIG. I;

FIG. 3 is an enlarged detailed view of a portion of the surface of thecathodic mold before it is coated with an electrically conducting film;

FIG. 4 is an enlarged detailed sectional view of a portion of thecathodic mold with a layer of metal electroformed on the mold;

FIG. 5 is a perspective view illustrating the part electroformed on themold of FIGS. 2-4 after it is removed from the mold;

FIG. 6 is a sectional view of an article of manufacture made by theelectroplating process of the present invention;

FIG. 7 illustrates a cathode made in accordance with a differentembodiment of the invention for electroforming a metal screen;

FIG. 8 is a sectional view of the cathode of FIG. 7 with the screenelectroformed on the cathode; and

FIG. 9 illustrates an enlarged view of a portion of a screenelectroformed by the cathode illustrated in FIGS. 7 and 8.

DETAILED DESCRIPTION OF THE INVENTION As shown in FIG. 1, a plaster formdesignated by the reference number 11 is made of the shape in which thepart is desired to electroformed. In the specific example illustrated,the part to be electroformed is an aircraft nose section approximatelyparabolic in shape and forming half of an aircraft nose. This part mightbe for example 10 feet long and measure 8 feet along the surface fromside to side. The surface 13 of the plaster form 11 is formed into thedesired shape of the part to be manufactured. This surface I3 is thencoated with a parting compound, which is preferably silicone oil and isdesignated by the reference number 14 in FIG. 2. A wire mesh or screen15 is then positioned overlying the entire surface 13. In this example,the screen is 54-inch mesh of 23 gage copper wire. Instead, fly screen,expanded metal mesh, or an interconnecting network of metal ribbonscould be used. The mesh is carefully set in place very close to thesurface 13 of the plaster form and may be impressed right to the surface13. A conventional epoxy mixture is then applied to the back of thescreen 15 filling in the interstices of the screen and any spaces whichexist between the screen and the surface 13, care being taken not todisplace the screen. A fiberglass cloth 16 is then placed over thescreen and an additional epoxy mixture is applied to the back of thefiberglass cloth coating and filling in the interstices of the cloth.This process is repeated with addi tional alternate layers of fiberglasscloth and epoxy until the structure is built up to the desiredthickness, which in the preferred embodiment is about a quarter of aninch. A tubular metallic or plastic structure may be added between or inback of the fiberglass layers in this process to rigidize and strengthenthe shape of the epoxy structure to facilitate its handling.

After the structure is built up to its desired thickness, it is cured ina conventional manner. The structure comprising the screen and thelaminated fiberglass bonded together by the epoxy resin is then removedfrom the plaster form 11 and will form the base of the cathodic moldover which the parts to be electroformed are electrodeposited. After themold has been removed from the plaster form fill, the surface of themold which conforms to the surface 13 of the plaster form Ill andadjacent which the screen 15 is positioned is lightly abraded (as bysanding) to expose portions of the screen H. The sanding is conducteduntil at least one half of the perimeter of each square of the screen 15is exposed and preferably until three quarters of the perimeter of eachscreen square is exposed.

FIG. 3 illustrates the surface of the mold after the sanding of thesurface has been carried out. The exposed portions of the screen aredesignated by the reference number 17 The resulting structure, aftersanding, is then cleaned and the surface containing the exposed portions17 is coated with an electrically conducting thin film, which may be asilver, copper or other conductive paint. Preferably, however, a silverreduction process is used. A solution of silver nitrate and formaldehydeis mixed together (in a ratio of approximately 200 g. of silver nitratefor each 200 cc. of formaldehyde) and sprayed over the surface. Themixing process is carried out in a nozzle just prior to the spraying togive a bright silver coating to the mold. This silver film is made verythin, just thick enough to entirely cover the surface of the mold. Thesurface coated with this film will be the surface on which theelectroforming is carried out and accordingly is referred to as theelectroforming surface.

Electrodeposition of metal is carried out by immersing theelectroforming surface in an electroforming bath, and conmeeting thescreen 15 to the negative side of a DC power source to render the moldcathodic. When these steps have been carried out and the anodes of thebath are connected to the positive side of the power source, metal willbe electrodeposited on the electrically conducting film. Thiselectrodeposition is continued until a layer of metal of the desiredthickness (which commonly will be at least one quarter of an inch ormore) is formed on the electrically conducting film. in the sectionalview in FIG, 4, the electrodeposited layer of metal is designated by thereference number 2i and the thin electrically conducting film isdesignated by the reference number 22. During this electrodeposition,current will be carried uniformly to all parts of the electroformingsurface of the mold by the screen 15 so the layer 2B of metal will growuniformly over the entire surface of the mold and high current densitiesin the conducting film of silver will be eliminated. In addition, theelectroformed layer 21 will grow to the desired thickness much morequickly than the systems of the prior art. Because the screen 15 carriesthe current, the thickness of the conducting film 22 can be reduced to aminimum measuring in microinches, thereby making possible a highfidelity of duplication.

One example of the electroforming bath to be used in this electroformingprocess and which provides copper electrodeposits is an aqueous solutionof about 25 to 100 (preferably 50) grams per liter of sulfuric acid andabout 100 to 300 (preferably 200) grams per liter of copper sulfate. Inthis example, the electroforming is carried out at room temperature orin the range of about 7590 F. and preferably at 80 F. The currentdensity at the surface of the anode should be in the range of to 40amperes per square foot and is preferably 30 amperes per square foot. At20 amperes per square foot, the electroformed layer 21 will growuniformly over the entire electroforming surface of the mold at a rateof about one-thousandths of an inch per hour. The anodes used in thisexample are soluble copper anodes.

In another specific example adapted to provide a nickel electro-deposit,the electrolytic bath is an aqueous solution of 300 grams per liter ofnickel sulfate and 50 grams per liter of boric acid with a pH of about4.2. The nickel sulfate may range between about 200-800 grams per literand the boric acid may range between about 35-75 grams per liter withthe pH ranging from about 3 to 4.5. The electrodeposition in thisexample is carried out preferably at a temperature of 120 F. but mayrange from 100 to 150 F. in this example, the

preferred current density over the cathode surface is 30 amperes persquare foot and may rangefrom 5-800 amperes per square foot. The anodesused are SD nickel chips in anode baskets. SD nickel chips aremanufactured by lntemational Nickel Company and are sulfur-containingnickel. The sulfur is added to the nickel to make the nickel moresoluble. Alternatively, cast carbon nickel anodes or depolarized nickelanodes could be used. The cast carbon nickel anodes contain carbon toincrease the solubility of the anodes and the depolarized anodes containoxygen to increase their solubility.

After the electroformed layer 21 has been built up to the desiredthickness, it is stripped from the mold and the thin silver film 22operates as a parting compound in the stripping operation. FIG. 5illustrates the aircraft nose section, electroforrned by the processillustrated in FIGS. 1-4.

The above described process may be also used with the same advantages toelectroplate large nonconducting surfaces in which the finished productcomprises the base of nonconducting material as well as theelectrodeposited layer. In the electroplating embodiment, the screen i5is embedded in the nonconducting surface to be electroplated and thesurface is lightly sanded to expose the nodes of the screen in the samemanner as described above. Also, as described above, a thin conductivefilm is applied to the surface to be electroplated. Then metal iselectrodeposited in an electrolytic bath on this electrically conductingsurface. FIG. 6 is a sectional view of a product made by thiselectroplating process. Typical applications of this process would befiberglass rotor blades, fiberglass propeller blades and fiberglassboats.

FIGS. 7 and 8 illustrate a method of electroforming a foraminous articlesuch as a screen in accordance with the present invention. As shown inthe figures, a stamped screen 25 is embedded in a nonconducting slab ofmaterial 27. This slab of nonconducting material may be laminatedfiberglass layers bound together and to the stamped screen 25 by anepoxy resin and may be formed in the same manner as the mold describedwith reference to FIGS. 1 and 2. The surface to which the screen 25 isadjacent is sanded to expose the entire outer surface of the screen inthe slab 27. The slab 27 is then placed in electrolytic bath, and anelectrical connection is made to the screen 25 connecting it as acathode so as to electrodeposit metal on the exposed conductingsurfaces. As a result, electrodeposition will take place in the form ofthe pattern of the electrically conducting portion in the surface of themember 27, in this case forming a screen. When the strands of the screenhave built up to the desired thickness, the slab 27 is removed from theelectrolytic bath and the electroformed screen is stripped away. FIG. isan enlarged fragmented view of the resulting electrodeposited screen.

It is to be noted that in the production of a forarninous article suchas a screen, where the entire outer conductor surface of the screen isexposed, it is not necessary as in the case of the other embodiments tocoat the conductors with an electrically conductive coating.

The above description is of preferred embodiments of the presentinvention and may modifications may be made thereof without departingfrom the spirit and scope of the invention which is defined in theappended claims.

What is claimed is:

l. A method of forming a layer of metal over a large nonconductingsurface comprising the steps of embedding a network of interconnectingelectrical conductors in said surface in a manner so that portions ofsaid conductors are exposed on said surface, coating said surface withan electrically conducting film whereby said film is in electricalcontact with said exposed portions of said conductors andelectrodepositing a layer of metal on said film.

2. A method of forming a layer of metal over a large nonconductingsurface as recited in claim 1 wherein said portions of said conductorsin said surface are exposed prior to the coating of said surface with aconducting film by abrading said surface.

3. A method of forming a layer of metal over a large nonconductingsurface as recited in claim 1 wherein said interconnecting conductorscomprise a screen.

4. A method of electroforming comprising the steps of making a mold ofnonconducting material defining a surface in the shape of the part to beelectroformed and having a network of interconnecting electricalconductors embedded in said surface with portions of said conductorsdistributed over said surface exposed on said surface, coating saidsurface with a film of electrically conducting parting compound,electrodepositing metal on said film, and recovering saidelectrodeposited metal from said mold.

S. A method of electroforming as recited in claim 4 wherein the exposedportions of said conductors in said nonconducting surface are made flushwith said surface prior to the coating of said surface with said film.

6. A method of electroforming as recited in claim 5 wherein saidportions of said conductors are exposed and made flush with said surfaceby abrading said surface.

7. A method of electroforming as recited in claim 4 wherein said networkof interconnecting conductors comprises a screen.

8. A method electroforming as recited in claim 4 wherein said step ofmaking said mold comprises setting said network of electrical conductorsadjacent to a surface defining the shape of the form of the part to beelectroformed, and then filling the interstices of said network ofelectrical conductors with a nonconducting material,

9. A method of electroforming as recited in claim 8 wherein said step ofmaking said mold further includes embedding a fiberglass cloth in saidnonconducting material behind said network of interconnecting electricalconductors.

10. A method of electrodepositing a layer of metal in a contoured shapecomprising making a base of nonconducting material defining a surface inthe form of said contoured shape and having a network of interconnectingelectrical conductors embedded in said surface with portions of saidconductors distributed over said surface exposed on said surface,coating said surface with an electrically conducting film andelectrodepositing metal on said film.

H. A method of electrodeposition as recited in claim 10 wherein saidstep of making said base comprises setting said network of electricalconductors adjacent to a surface defining said contoured shape and thenfilling the interstices of said network of electrical conductors with anonconducting material.

112. A method of electrodeposition as recited in claim 11 wherein saidstep of making said base further includes embedding a fiberglass clothin said nonconducting material behind said network of interconnectingelectrical conductors.

13. An electroplated article of manufacture comprising a base ofnonconducting material defining a molded surface, a network ofinterconnecting electrical conductors which are in physical andelectrical contact with each other and embedded in and distributed oversaid surface, and having portions thereof exposed in said surface, alayer of conducting material covering said molded surface, and anelectrodeposited layer of metal covering the layer of conductingmaterial which is in electrical contact with said network of electricalconductors.

M. An electroplated article as recited in claim 13 wherein said networkof electrical conductors comprises a screen.

15. An electroplated article as recited in claim 13 wherein a film ofelectrically conducting material is sandwiched between said layer ofmetal and said network of conductors providing electrical connectionbetween said layer and said conductors.

2. A method of forming a layer of metal over a large nonconductingsurface as recited in claim 1 wherein said portions of said conductorsin said surface are exposed prior to the coating of said surface with aconducting film by abrading said surface.
 3. A method of forming a layerof metal over a large nonconducting surface as recited in claim 1wherein said interconnecting conductors comprise a screen.
 4. A methodof electroforming comprising the steps of making a mold of nonconductingmaterial defining a surface in the shape of the part to be electroformedand having a network of interconnecting electrical conductors embeddedin said surface with portions of said conductors distributed over saidsurface exposed on said surface, coating said surface with a film ofelectrically conducting parting compound, electrodepositing metal onsaid film, and recovering said electrodeposited metal from said mold. 5.A method of electroforming as recited in claim 4 wherein the exposedportions of said conductors in said nonconducting surface are made flushwith said surface prior to the coating of said surface with said film.6. A method of electroforming as recited in claim 5 wherein saidportions of said conductors are exposed and made flush with said surfaceby abrading said surface.
 7. A method of electroforming as recited inclaim 4 wherein said network of interconnecting conductors comprises ascreen.
 8. A method electroforming as recited in claim 4 wherein saidstep of making said mold comprises setting said network of electricalconductors adjacent to a surface defining the shape of the form of thepart to be electroformed, and then filling the interstices of saidnetwork of electrical conductors with a nonconducting material.
 9. Amethod of electroforming as recited in claim 8 wherein said step ofmaking said mold further includes embedding a fiberglass cloth in saidnonconducting material behind said network of interconnecting electricalconductors.
 10. A method of electrodepositing a layer of metal in acontoured shape comprising making a base of nonconducting materialdefining a surface in the form of said contoured shape and having anetwork of interconnecting electrical conductors embedded in saidsurface with portions of said conductors distributed over said surfaceexposed on said surface, coating said surface with an electricallyconducting film and electrodepositing metal on said film.
 11. A methodof electrodeposition as recited in claim 10 wherein said step of makingsaid Base comprises setting said network of electrical conductorsadjacent to a surface defining said contoured shape and then filling theinterstices of said network of electrical conductors with anonconducting material.
 12. A method of electrodeposition as recited inclaim 11 wherein said step of making said base further includesembedding a fiberglass cloth in said nonconducting material behind saidnetwork of interconnecting electrical conductors.
 13. An electroplatedarticle of manufacture comprising a base of non-conducting materialdefining a molded surface, a network of interconnecting electricalconductors which are in physical and electrical contact with each otherand embedded in and distributed over said surface, and having portionsthereof exposed in said surface, a layer of conducting material coveringsaid molded surface, and an electrodeposited layer of metal covering thelayer of conducting material which is in electrical contact with saidnetwork of electrical conductors.
 14. An electroplated article asrecited in claim 13 wherein said network of electrical conductorscomprises a screen.
 15. An electroplated article as recited in claim 13wherein a film of electrically conducting material is sandwiched betweensaid layer of metal and said network of conductors providing electricalconnection between said layer and said conductors.